She's human..
Wouldn't you feel bad leading on a guy when you know that you don't have feelings for him, yet he believes you do?
She feels bad because it's wrong to make people believe you like them when really you don't, and it's worse because she realises how attached MP is towards her.
No matter how bad a person is I wouldn't lead them on or play with their feelings, and I think it is the same for her. It doesn't mean she likes him in a romantic way.